I usually install Debian Linux on old Chromebooks that have only 16 GB SSD, and then gift them to my cousins or their kids. Flatpacks are out of the question, since pretty much every app I checked is between 500 and 1 GB of size. I only have 7.5 GB of free space in there after the base XFce Debian installation is done, plus 2 GB of swap. I find flatpacks to be space eaters, and I avoid them even on my normal, higher SSD size laptops.